Gallien-Krueger 800RB questions

This weekend in my continuing search for a warm, relatively small, portable rig I visited Rock City Guitars in Somerville, Massachusetts. Justin had his portable rig in the store: a 1970s Alembic preamp through the power section of a GK 800RB and then into various cab combinations. I searched the archives and it seems a few people on TB do this as well. That makes a lot of sense, because if the pre goes down there's still a fully-functioning amp. So my latest notion is to get an Aguilar, Ampeg or some other preamp, an older 800RB and either a Bergantino or Aguilar 1x15 cabinet.

I'm curious if the 800RB can handle the a 5-string bass? Some of the newer GK heads have a 4/5 switch. Will this even matter when I use the 800RB as a power amp only? Also, is anyone using this amp with a 1x15 cabinet, specifically the Aggie or Berg?

BTW, Rock City is such a nice shop. They had vintage Ampegs, an Acoustic, a Sunn in stock, a Sadowsky Tokyo, two Atelier Z 5-strings, a row of cool Fenders. Justin hung out with my brother and me well after closing time, just shooting the breeze, talking about music and the bass.

I've been using a 5 string with my 800rb
for years with no problems. As you may have
seen in other threads, I use my Tyler 5 through
either a Fodera or Sadowsky preamp, into the
effects return of my GK. Works great! I also use
my bass straight into the amp too. All depends on
the sound i'm looking for, and the music.